What's All This About Weather Helm?|
Exploring One of Life's Great Mysteries.
By Kim Miller
The How-To Guide
Mast Rake refers to the angle of attack of the mast. If it upright is has no rake, if it slopes backwards so that the top of the mast is over or behind the rear cross beam is has extreme rake. If it points forward, well, it shouldn't point forward. One of the discoveries of the racing world is that having extreme mast rake makes the boat go faster. Extreme mast rake causes unwanted side effects, but the speed gain is worth it. Some of those side effects can be compensated for by adjusting other boat parts, particularly the rudders.
When your Hobie left the factory it was set with the mast at a pre-determined angle. As with many things, that angle might not be the most suitable for your kind of sailing. The angle of the mast is controlled by the length of the forestay. As the forestay is lengthened the mast tilts backwards. And as the mast tilts backwards the side stays become loose and have to be adjusted back to a suitable tension by shortening their effective length.
How far should I rake my mast?
If you want to get maximum speed from your Hobie the mast will want to be raked back as far as possible. This is not as radical as it sounds. There is a limit to how far you can rake it anyway. This limit is caused by the mainsheet blocks. As you rake the mast the outer end of the boom tilts towards the deck. This makes the mainsheet blocks come closer together. You can't rake the mast beyond that point of the blocks touching each other.
However, you still want some control over mast bend with the mainsheet, so you can only have the blocks touching after you have maximum operating tension on the mainsheet. This limits the mast rake again. If you have too much rake the blocks will touch before any mast bend is induced. This limit is measured when the boom is centred.
The most extreme rake you can put on the mast is when the blocks are just touching when you have pulled on the mainsheet as hard as you ever need to while sailing, generating maximum mast bend in the process.
How do I rake my mast?
You rake the mast by lengthening the forestay. The easiest way to do this is to add a short length of rigging cable called a strop at the top or bottom of the forestay. It is not a difficult process to get the length of the strop.
You will need two people. One stands on the trampoline and holds the
mast from behind.
You have now reached the maximum mast rake point. There is no value in going further than this. However, you could easily decide in the future that you want to reduce the rake, so you can add adjustability by shortening the strop and added an adjusting plate while maintaining the overall length. Remember that the plate will have to begin life at maximum length so you can adjust it shorter if necessary. Instead of a cable strop you can add a stainless steel strip with adjusting holes in it.
Now you have to get the new length of the side stays. Your existing stays will have to be shortened, or you might like to have new ones made. The shortened length is easily worked out by measuring the amount of slack that has developed as the mast tilted back. Just cut that slack out of the stays and swage new thimbles onto the lower end. Remember that if you decide to reduce mast rake the side stays will lengthen, so cut the new length so that with full rake the adjuster plates are at their shortest. This way you can lengthen them as the mast moves forward if needed in the future. Keep both stays as equal as possible when measuring and cutting.
If you are not familiar with how to cut the stays, or with how to swage new fittings, or you do not have the proper tools, (parrot beak cutters and a suitable sized swaging tool) do not do this work yourself. It is easy to measure it up, remove the stay, and have the sail shop do it for you. And it is a lot safer as well.
How long should my stays be?
Unfortunately there is no real answer to this question. It will depend
on your desired angle of mast rake, on the length of the bridle, on the
length of the shackles you are using, on whether you have a jib furler
or not, on the position of the mast tang. There are too many variables
to give a set length. Two boats coming from the factory are the same, but
in a year or two one of them could easily have had some modification that
makes a difference. Even just replacing a lost shackle with a longer one
floating around in the sail bag can make a difference.
Unfortunately, one of the side effects of extreme mast rake is that the rudders become harder to manage because of the extra weather helm and "tiller tug" induced by the new boat balance. You can make the boat easier to control by raking the rudders forward. There are several ways to do this.
Rudder rake adjusting screws.
Re-drilling rudder positioning holes.
Taking up cam slack.
The go-faster guys tell us that the boat works best with a slight amount of toe-in to the rudders. Here's how to measure it. With the boat on the trailer lock the rudders in the down position. Get a tape measure and a helper to steady the rudders. Tie the tiller cross bar so the rudders can't move sideways too much.
Measure the distance across the boat between the leading edges of the rudders. Now measure between the trailing edges The measure point is where the rudder has the widest fore/aft distance. The leading edge distance should be about a quarter inch shorter than the trailing edge distance.
The adjustment is made at one end of the tiller crossbar, where it fastens to the little casting joints. It is more likely that you do not have toe-in and the tiller crossbar has to be shortened. If you already have excess toe-in the crossbar has to be lengthened. This is a headache, but not impossible.
Once again, the newer boats have an adjustable system, and the older
boats don't. If you have an adjustable tiller crossbar you can unlock one
end and screw it in or out until the toe-is is set correctly. If
you do not have an adjustable tiller crossbar you will need to drill out
the pop rivets from one end of the crossbar, cut it to length, and replace
If you you need to lengthen the crossbar you need a piece of tube that neatly fits inside the existing piece. Then you cut your crossbar, fit this new piece inside and pop rivet one end. Then measure again to locate where the other end should be pop riveted together. Doing things this way can leave edges that your hand will not like to run over when sailing, so put this extra piece as close to the center of the crossbar, not at the ends where you are more likely to hold on to it. Tape it over with duct tape when you are done.
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